FIGS. 1A and 1B illustrate one type of prior art switch panel device which comprises a switch panel 11 mounted to a housing 10, for example, of an electronic equipment so as to close the front opening thereof. The switch panel 11 comprises a frame 12 having an array of switch elements 13 secured thereto such that the "keytops" or operating ends 13a of the switch elements 13 project beyond the outer face or front face of the switch panel 11.
Applied to that side of the frame 12 from which the operating ends 13a project is a sheet 14 on which there are printed indicia 15 such as characters, symbols, figures or the like for identifying the switch elements 13. The indicia 15 are positioned adjacent to the operating ends 13a of the respective switch elements such that they are not interfered with by the operating ends.
FIG. 1C shows another type of prior art switch panel device which comprises a touch switch sheet 17 applied to the screen of a CRT display 16 which is in turn mounted in a housing 10 with the screen facing toward the front opening of the housing. The touch switch sheet 17 comprises a transparent sheet and transparent electrode switches (touch switches) arranged thereon in an array. Characters or symbols for identifying the respective touch switches are displayed on the CRT display 16 at the portions thereof corresponding to the respective touch switches of the touch switch sheet 17.
FIG. 1D illustrates still another type of switch panel device utilizing an LCD display 18 in place of the CRT display 16. While not shown in the drawings, it is conceivable to eliminate the sheet 14 in FIGS. 1A and 1B and embed LCD's in the respective keytops 13a to display the indicia for designating the respective keytops 13a.
In the case of the conventional switch panel 11 shown in FIGS. 1A and 1B, when the user calls for a custom-made switch panel 11 having altered indicia 15 applied thereto for designating the switch elements, the manufacturer is required to prepare a new switch panel having a sheet 14 printed with the altered indicia 15, which takes time before the new switch panel is delivered to the user.
The manufacturer may have a number of preliminarily-made switch panels in stock in order to cope with users' calls for short time delivery. However, if none of the switch panels manufactured in advance should meet s user's request for modified indicia, it would be required to remove a sheet 14 from one of the switch panels in stock to replace it by a new sheet having the modified indicia printed thereon, which is a time-consuming task.
In addition, the working face of the switch panel 11 is usually compelled to have a planar surface due to limitations imposed by the flexibility and application properties of the sheet 14, resulting in difficulties in realizing a variety of designs of the switch panel as utilizing curved surfaces as required.
With the construction utilizing s CRT display 16 and a transparent touch switch sheet 17 as a switch panel as illustrated in FIG. 1C, it was difficult to reduce the depth of the device because of the CRT display 16 in a relatively small-size switch panel device.
With the switch panel device comprising an LCD 18 as illustrated in FIG. 1D, the use of a wide panel makes the device highly expensive if the indicia are to be displayed in colors.
In the switch panel device having LCD's embedded in the keytops, the LCD's, one being embedded in each of keytops, not only requires a complicated image displaying circuit, but also makes the device very expensive if the display is to be colored.